• Introduction
• Matrix New!
• Glossary New!
• Notice

• Environmental and Engineering Evaluation New!
• State Contacts New!
• Cost Issues
• Standards/Specifications New!

• Baghouse Fines
• Blast Furnace Slag
• Coal Bottom Ash/Boiler Slag Updated!
• Coal Fly Ash Updated!
• FGD Scrubber Material Updated!
• Foundry Sand Updated!
• Kiln Dusts
• Mineral Processing Wastes
• MSW Combustor Ash
• Nonferrous Slags
• Quarry Byproducts
• Reclaimed Asphalt Pavement Updated!
• Reclaimed Concrete Material Updated!
• Roofing Shingle Scrap Updated!
• Scrap Tires
• Sewage Sludge Ash
• Steel Slag
• Sulfate Wastes
• Waste Glass

• General Descriptions
• Asphalt Concrete Pavement
• Portland Cement Concrete Pavement
• Granular Base
• Embankment or Fill
• Stabilized Base
• Flowable Fill

[ Material Description ] - [ Portland Cement Concrete ] - [ Granular Base ] - [ Embankment or Fill ]

RECLAIMED CONCRETE MATERIALMaterial Description

ORIGIN

Two billion tons of aggregate are produced every year in the US. Production of aggregate is expected to reach 2.5 billion tons by 2020, which raises concerns about where the new aggregate will come from ⁽⁵⁾ . One alternative to using virgin aggregate is recycled concrete aggregate. Recycled concrete aggregate (RCA) consists of high-quality, well-graded aggregates (usually mineral aggregates), bonded by a hardened cementitious paste. The aggregates comprise approximately 60 to 75 percent of the total volume of concrete.

RCA is generated through the demolition of Portland cement concrete elements of roads, runways, and structures during road reconstruction, utility excavations, or demolition operations.

In many metropolitan areas, the RCA source is from existing Portland cement concrete curb, sidewalk and driveway sections that may or may not be lightly reinforced. The RCA is usually removed with a backhoe or payloader and is loaded into dump trucks for removal from the site. The RCM excavation may include 10 to 30 percent subbase soil material and asphalt pavement. Therefore, the RCA is not pure Portland cement concrete, but a mixture of concrete, soil, and small quantities of bituminous concrete.

The excavated concrete that will be recycled may be hauled to a central facility for stockpiling and processing or processed on site using a mobile plant. During processing crushing, screening, and ferrous metal recovery operations occur. Present crushing systems, with magnetic separators, are capable of removing reinforcing steel without much difficulty. Welded wire mesh reinforcement, however, may be difficult to remove.

In 2004 the Federal Highway Administration conducted a five state scanning tour to review the state of the art with regard to the use of reclaimed concrete ⁽⁵⁾. The final report provides valuable information regarding current practices for using RCA.

Additional information on recycling of reclaimed concrete material can be obtained from the following organization:

Construction Materials Recycling Association
P.O. Box 122
Eola , IL 60519
www.cdrecycling.org
www.concreterecycling.org

CURRENT MANAGEMENT OPTIONS

Recycling

Recycling concrete is on the rise and saves valuable resources, especially when the RCA is recycled and reused within the same metropolitan area, cutting down on fuel emmisions ^(2,3,5) . Recycling RCA has proven to be very cost effective ⁽⁶⁾ . RCA can be used as an aggregate for cement-treated or lean concrete bases, a concrete aggregate, an aggregate for flowable fill, or an asphalt concrete aggregate. It can also be used as a bulk fill material on land or water, as a shore line protection material (rip rap), a gabion basket fill, or a granular aggregate for base and trench backfill.

The interactive recycling map below shows where reclaimed concrete material is used in various applications including using it as aggregate, aggregate base, and using it in Portland cement concrete (PCC).

Disposal in landfills, near the right-of-way, and in borrow pits or depleted quarries has historically been the most common method of managing RCA. However, recycling has become a more attractive option, particularly in aggregate-scarce areas and in large urban areas where gathering and distribution networks for RCA have been developed.

MARKET SOURCES

RCA can usually be obtained from central processing plants where the processed material is stockpiled and sold. Well-processed RCA will normally yield consistent physical properties, but RCA properties can sometimes vary depending on the properties of the quality of the recovered concrete.

Variations between concrete types result from differences in aggregate quality, aggregate size, concrete compressive strength, and uniformity. ⁽⁹⁾ For instance, aggregates in concrete not exposed to severe weathering (such as footings and covered structural members) can contain a higher proportion of deleterious substances than those in pavement concrete. Precast concrete generally has smaller aggregate size, higher compressive strength, and less variation in strength and other properties than cast-in-place concrete. Some recycled pavements may show evidence of distress from alkali-silica reaction due to the presence of a siliceous aggregate with reactive constituents. In areas where deicing salts are extensively used, recycled concrete may contain relatively high levels of chlorides.

HIGHWAY USES AND PROCESSING REQUIREMENTS

Aggregate Substitute

The use of RCM as an aggregate substitute in pavement construction is well established, and includes its use in granular and stabilized base, engineered fill, and Portland cement concrete pavement applications. Other potential applications include its use as an aggregate in flowable fill, hot mix asphalt concrete, and surface treatments.

To be used as an aggregate, RCA must be processed to remove as much foreign debris and reinforcing steel as possible. Reinforcing steel is sometimes removed before loading and hauling to a central processing plant. Most processing plants have a primary and secondary crusher. The primary crusher (e.g., jaw crusher) breaks the reinforcing steel from the concrete and reduces the concrete rubble to a maximum size of 75 mm (3 in) to 100 mm (4 in). As the material is conveyed to the secondary crusher, steel is typically removed by an electromagnetic separator. Secondary crushing further breaks down the RCM, which is then screened to the desired gradation. To avoid inadvertent segregation of particle sizes, coarse and fine RCM aggregates are typically stockpiled separately.

MATERIAL PROPERTIES

Physical Properties

Processed RCA, which is 100 percent crushed material, is highly angular in shape. Due to the adhesion of mortar to the aggregates incorporated in the concrete, processed RCA has rougher surface texture, lower specific gravity, and higher water absorption than comparatively sized virgin aggregates. As processed RCA particle size decreases, there is a corresponding decrease in specific gravity and increase in absorption, due to the higher mortar proportion adhering to finer aggregates. High absorption is particularly noticeable in crushed fine material, which is less than 4.75 mm in size (minus No. 4 sieve size), and particularly in material from air-entrained concrete (since there is substantially more air-entrained mortar in the fine than the coarse RCA aggregates). The minus 0.075 mm (No. 200 sieve) fraction is usually minimal in the RCA product. Some typical physical properties of processed RCA are listed in Table 1.

Processed RCA is generally more permeable than natural sand, gravel, and crushed limestone products. ⁽⁶⁾

Table 1. Typical physical properties of processed reclaimed concrete material. ⁽¹⁾

Chemical Properties

The cement paste component of RCA has a substantial influence on RCA alkalinity. Cement paste consists of a series of calcium-aluminum-silicate compounds, including calcium hydroxide, which is highly alkaline. The pH of RCA-water mixtures often exceeds 11.

RCA may be contaminated with chloride ions from the application of deicing salts to roadway surfaces or with sulfates from contact with sulfate-rich soils. Chloride ions are associated with corrosion of steel, while sulfate reactions lead to expansive disintegration of cement paste. RCA may also contain aggregate susceptible to alkali-silica reactions (ASR). When incorporated in concrete, ASR-susceptible aggregates may cause expansion and cracking.

The high alkalinity of RCA (pH greater than 11) can result in corrosion of aluminum or galvanized steel pipes in direct contact with RCA and in the presence of moisture. Similarly, RCA that is highly contaminated with chloride ions can lead to corrosion of steel.

Mechanical Properties

Processed coarse RCA, which is greater than 4.75 mm in size (No. 4 sieve size), has favorable mechanical properties for aggregate use, including good abrasion resistance, good soundness characteristics, and bearing strength. Typical mechanical properties are given in Table 2. Los Angeles Abrasion loss values are somewhat higher than those of high-quality conventional aggregates. Magnesium sulfate soundness and California Bearing Ratio (CBR) values are comparable to conventional aggregates.

Table 2. Typical mechanical properties of reclaimed concrete material .

The results of a 6-year Long Island, New York, study of materials processed from uncontrolled stockpiles for use as a granular subbase or base, presented in Table 3, reveal that physical properties such as magnesium sulfate soundness, Los Angeles Abrasion, density, and CBR of processed RCA are very consistent and can be expected to fall within a predictable range of values. ⁽³⁾

Table 3. 6-year study of RCM from uncontrolled stockpiles on Long Island , NY ⁽³⁾

ENVIRONMENTAL CONSIDERATIONS

For RCA, environmental considerations have focused on leachability of contaminants and pH changes from RCA storage and use. Previous research conducted on the leachability Portland cement concrete used the Toxicity Characteristic Leaching Procedure ⁽¹⁰⁾. Although leachability results were low ⁽¹⁰⁾, the TCLP simulates a municipal landfill setting and not a beneficial use environment, so results would not be applicable to environmental considerations for beneficial use. More recent research employed a serial batch test (Dutch Pre-Standard NVV 5432) ⁽¹¹⁾. This research concluded that well-cured Portland cement concrete released no detectable concentrations of antimony, arsenic, beryllium, cadmium, chromium, lead, mercury, nickel and selenium ⁽¹¹⁾. The internal alkaline nature of concrete is well known, but can change over time with weathering and age for numerous reasons (e.g., carbonation). RCA could also be alkaline, with potential pH values and changes similar to in-place concrete. Research conducted at Washington State University found that disposing of diamond grinding concrete slurry increased soil pH from 6.3 – 7.5 to 7.6 – 9.4 in once location and from 7.1 – 7.2 to 7.1 – 8.2 in a second location ⁽¹²⁾. Research conducted by the Ohio Department of Transportation and Iowa Department of Transportation found that the pH of RCA decreased little over time (was initially greater than 11 then decreased over time but remained above 9). The Ohio research concluded that using RCA as an aggregate base in low lying or wet areas where alkaline run-off would be likely to occur could have an adverse effect on the environment ⁽¹³⁾. The Iowa report found that the high pH of the drainage water from RCA use can kill or impede grass growth at a drain outlet ⁽¹⁴⁾. Texas has also completed research in using RCA in mechanically stabilized earth (MSE) berms that involved thorough material characterization, pH measurements and an evaluation of use ^(15,16). They concluded that pH and resistivity specifications for MSE wall backfill materials should be waived for crushed concrete, concrete structures that have suffered sulfate attack should not be crushed and used as backfill in MSE walls, and MSE walls with crushed concrete backfill should include adequate drains and high permittivity filter fabrics behind the wall to avoid drainage problems ⁽¹⁶⁾. The potential for a pH and drainage issues leads some jurisdictions to require that RCA stockpiles be separated (a minimum distance) from water courses.

REFERENCES

1. ACPA. Concrete Paving Technology : Recycling Concrete Pavement, American Concrete Pavement Association, Skokie , Illinois , 1993.
2. ECCO. In-Place Concrete Pavement Recycling Makes a Green Statement, Environmental Council of Concrete Orgainzations, 1997.
3. ECCO. Recycling Concrete Saves Resources, Eliminates Dumping, Environmental Council of Concrete Orgainzations, 1997.
4. ECCO. Recycling Concrete and Masonry, Environmental Council of Concrete Orgainzations, 1998.
5. FHWA, Transportation Applications of Recycled Concrete Aggregate, FHWA State of the Practice National Review, September 2004.
6. Hanks, A. J. and E. R. Magni. The Use of Recovered Bituminous and Concrete Materials in Granular Base and Earth, Report MI-137, Ontario Ministry of Transportation, Downsview, Ontario 1989.
7. Personal Correspondence, Richard Petrarca, Twin County Recycling, Hicksville , New York , 1995
8. Petrarca, R.W. and V.A.Galdiero. "Summary of Testing of Recycled Crushed Concrete," Transportation Research Record No. 989 , pp. 19-26, Washington , DC , 1984.
9. Yrjanson, William A. Recycling of Portland Cement Concrete Pavements , National Cooperative Highway Research Program Synthesis of Highway Practice No. 154, National Research Council, Washington , D.C. , December, 1989.
10. Kreitch, A.J. Leachability of Asphalt and Concrete Pavements, Heritage Research Group Report, Indianapolis, Indiana , March 1992.
11. Hilliera, S.R., Sangha, C. M., Plunkettb, B. A., Waldena, P. J., Long-term leaching of toxic trace metals from Portland cement concrete, Cement and Concrete Research, Vol. 29, p. 515-521, 1999.
12. Shanmugam, Harini, Assessment and mitigation of potential environmental impacts of Portland Cement Concrete highway grindings, Thesis, Washington State University, 2004.
13. Ohio Department of Transportation, Recycled Materials Report, Box Test.
14. Steffes, R., Laboratory Study of the Leachate from Crushed Portland Cement Concrete Base Material, Iowa Department of Transportation, September 1999.
15. Ellen M. Rathje, Alan F. Rauch, Kevin J. Folliard, David Trejo, Dallas Little, Chirayus Viyanant, Moses Ogalla, Michael Esfelle, Recycled Asphalt Pavement and Crushed Concrete Backfill: State-of-the-Art Review and Material Characterization, Center for Transportation Research at The University of Texas at Austin, Texas Department of Transportation, Octboer, 2001.
16. Rathje, E., Rauch, A., Trejo, D., Folliard, K., Viyanant, C., Esfellar, M. Jain, A., Ogalla, M., Evaluation of Crushed Concrete and Recycled Asphalt Pavement as Backfill for Mechanically Stabilized Earth Walls, Center for Transportation Research at The University of Texas at Austin, Texas Department of Transportation, March 2006.

[ Material Description ] - [ Portland Cement Concrete ] - [ Granular Base ] - [ Embankment or Fill ]